Question

Suppose one has about 50,000 different .cpp files.

Each .cpp file contains just one class that has about ~1000 lines of code in it (the code itself is not complicated — involves in-memory operations on matrices & vectors — i.e, no special libraries are used).

I need to build a project (in a Linux environment) that will have to import & use all of these 50,000 different .cpp files.

A couple of questions come to mind:

1. How long will it roughly take to compile this? What will be the approx. size of the compiled file?
2. What would be a better approach — keep 50,000 different .so files (compiled extenstions) and have the main program import them one by one, or alternatively, unite these 50,000 different .cpp files into one large .cpp file, and just deal with that? Which method will be faster / more efficient?

Any insights are greatly appreicated.

Answer 1

(i) There are way too many factors involved in determining this, even an approximation is impossible. Compilation can be memory, cpu or hard drive bound. The complexity of the files matter (from your description, your complexity is low).

(ii) The typical way of doing this is to make a library and let the system figure out linking or loading. You can choose static or dynamic linking.

static linking
Assuming you are using gcc, this would look like this:
g++ -c file1.cpp -o file1.o
g++ -c file2.cpp -o file2.o
...
g++ -c filen.cpp -o filen.o
ar -rc libvector.a file1.o file2.o ... filen.o

Then, when you build your own code, your final link looks like this:

g++ myfile.cpp libvector.a -o mytask

dynamic linking
Again, assuming you are using gcc, this would look like this:

g++ -c file1.cpp -fPIC -o file1.o
g++ -c file2.cpp -fPIC -o file2.o
...
g++ -c filen.cpp -fPIC -o filen.o
ld -G file1.o file2.o ... filen.o -o libvector.so

Then, when you build your own code, your final link looks like this:

g++ myfile.cpp libvector.so -o mytask
You will need libvector.so to be in the loader’s path for your executable to work.

In any case, as long as the 50,000 files don’t change, you will only need to do the last command (which will be much faster).